Intramammary infections (IMI) are common in non-lactating heifer and dry cow mammary glands and occur during periods of appreciable mammary growth and development. The presence of these infections is expected to negatively impact mammary growth and development but has yet to be investigated. The works reported here investigated how IMI affects mammary tissue structure, cellularity, and the expression of integral mammogenic hormone receptors implicated in mammary growth. Non-pregnant non-lactating cows (n = 19) were administered estradiol and progesterone to stimulate mammary growth and 2 quarters of each cow were subsequently infused with either saline (n = 19) or Staphylococcus aureus (n = 19). Intramammary infusion of Staphylococcus aureus increased the number of immune cells present in gland secretions and also increased the proportion of neutrophils comprising these secretion somatic cells. Mammary tissues from quarters infused with Staphylococcus aureus contained more immune cells, less mammary epithelial tissue area, and greater tissue areas of intralobular stromal tissue than saline quarters. Staphylococcus aureus quarters also contained more apoptotic mammary epithelial cells and a lower proportion of apoptotic cells in the intralobular stroma compartment than saline infused quarters; this signified that Staphylococcus aureus quarters had less epithelial growth and experienced an expansion and/or lack of regression of stromal tissues. The number of cells expressing estrogen receptor α (ESR1) and progesterone receptor (PGR), as well as staining characteristics of ESR1 and PGR positive nuclei was also examined in these tissues. No appreciable differences were observed in any of the examined ESR1 and PGR measures between Staphylococcus aureus and saline mammary glands, but myoepithelial cells from Staphylococcus aureus glands had a greater nuclear staining area than saline quarters, indicating that these cells were affected by IMI. The results of these investigations indicate that IMI, in mammary glands that are concurrently stimulated to grow and develop, limits the growth of mammary epithelium and impairs regression of the stromal tissue, both of which are necessary for successful lactational performance. / PHD / Successful growth and development of the dairy cow udder (mammary gland) is important and has long-term impacts on milk production. Most mammary growth occurs during the first pregnancy but, at this same time, a bacterial infection can be present within the mammary gland and is expected to hinder normal growth and development. The studies conducted here sought to examine how a bacterial infection, within a cow’s udder, affects mammary gland growth and development. Overall, it was observed that a bacterial infection in the mammary gland reduced the amount of functional tissue that would eventually produce milk while simultaneously increasing the amount of connective tissue. Infected mammary glands also had a greater number of dying mammary cells, reducing the number of cells that would eventually produce milk. Estrogen and progesterone are known to be integral in supporting mammary growth, so an examination of the number of cells being able to receive signals from estrogen and progesterone was also undertaken; presence of an infection did not alter the number of cells able to receive estrogen and progesterone’s signal. This work furthered our understanding of how bacterial infections affect mammary tissue and alter normal developmental processes.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/96306 |
| Date | 24 August 2018 |
| Creators | Enger, Benjamin David |
| Contributors | Dairy Science, Akers, Robert Michael, Nickerson, Stephen C., Petersson-Wolfe, Christina S., Corl, Benjamin A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
Page generated in 0.0022 seconds